Gas generating device

Abstract: A gas generator (30) of a gas generating device (100) is held by a cover (34) within a housing (11) of a webbing pretensioner (10). The cover (34) defines therethrough a hammer pin insertion hole (35). The hammer pin insertion hole (35) has an inner diameter smaller than the outer diameter of a fastening member such as a self-tapping screw (39) or that of a tool such as a screw driver, which is to be employed upon assembly and/or mounting of the gas generating device (100). This has made it possible to avoid accidental insertion of the fastening member or the tool into the hammer pin insertion hole (35) in the course of the assembling or mounting work and hence, to prevent a detonator (33) of the gas generator (30) from being accidentally struck.

Description: This invention relates to a gas generating device for actuating a safety apparatus such as an air bag system or a webbing pretensioner of a seat belt system, for example, in the event of an emergency such as a collision of an automotive vehicle so that an occupant can be protected. JP-A-05 154371, which describes a gas generating device according to the preamble of claim 1, discloses a gas generating device of this kind, comprising a gas generator having a detonator for being fired when struck by a hammer pin and a hammer pin trigger device for causing said hammer pin to strike said detonator in the event of an emergency, wherein the gas generator has a cover arranged to substantially close up the gas generator on the side of the hammer pin trigger device and defining therethrough a hammer pin insertion hole, into which the hammer pin is inserted. The hammer pin has a small-diameter portion located on the side of the detonator and a large-diameter portion on the side opposite to the detonator, which large-diameter portion is provided for supporting a spring by which the hammer pin is biassed to strike the detonator. Further, a spring-biassed lever is provided for holding the hammer pin in a starting position, wherein the lever engages the large-diameter portion of the hammer pin opposite to the spring biassing the hammer pin. Gas generating devices are available in two types, one being electrically fired and the other mechanically fired. Mechanical devices are however finding increasing popularity in recent years for their simpler construction and lower price. Referring first to FIGS. 3 and 4, a description will hereinafter be made of a conventional mechanically-triggered gas generating device as applied to a pretensioner of a webbing retractor in an automotive seat belt system. FIG. 3 is a cross-sectional view of the conventional gas generating device as applied to the webbing pretensioner, and FIG. 4 is a cross-sectional view illustrating a problem inherent to the conventional gas generating device. As is illustrated in FIG. 3, a frame 1 of a webbing retractor (not shown) for an unillustrated automotive vehicle, said frame having been formed by bending a steel plate, has a bracket 2 for mounting a gas generating device 90 on the webbing retractor. A pretensioner 10 and a hammer pin trigger device 20 are arranged on left-hand and right-hand side walls of the bracket 2 as viewed in the figure. The pretensioner 10 and the hammer pin trigger device 20 are fixed together by bolts 29, with the bracket 2 being held therebetween. The pretensioner 10 is equipped with a substantially cylindrical housing 11 fixed on the bracket 2 and a cylinder 13 threadedly secured in an end portion of the housing 11 and extending upwardly. A gas compartment 12 inside the housing 11 and a chamber 14 inside the cylinder 13 are in mutual communication, and a piston 15 is slidably fitted in the cylinder 13. A wire cable 16 which is wound on a take-up spindle of the unillustrated webbing retractor is connected at a free end thereof to the piston 15. A gas generator 30 is accommodated in an end portion of the housing 11, said end portion being on a side of the bracket 2. This gas generator 30 has a stepped, bottom-closed cylindrical casing 31, a gas generating chemical reagent 32 sealed in the casing 31, and a detonator 33 for firing the gas generating chemical reagent 32. The gas generator 30 is in threaded engagement with the housing 11 and, by a cover 37 substantially closing up a bracket-side opening of the housing 11, is held within the housing 11. The hammer pin trigger device 20 has, as is depicted in FIG. 3, a bottom-closed cylindrical housing member 21 mounted on the bracket 2, an unillustrated hammer pin trigger mechanism equipped with an inertia member (not shown) accommodated within the housing member 21 for displacement upon application of a deceleration of at least a predetermined value thereon in the event of a collision, a hammer pin 27 disposed displaceably by the hammer pin trigger mechanism, a spacer 26 made of a metal or resin and defining a through-hole in which the hammer pin 27 is slidably and supportedly fitted, and a hammer pin side cover 25 disposed in an opening of the housing member 21 and covering and holding the hammer pin trigger mechanism and the spacer 26 within the housing member 21. Operation of the above-described webbing pretensioner will next be described. Upon application of a deceleration of at least a predetermined value on the hammer pin trigger device 20 by a collision of an automotive vehicle or a like cause, the unillustrated inertia member causes the hammer pin 27 to displace so that the hammer pin 27 strikes the detonator 33. The detonator 33 so struck by the hammer pin 27 is ignited to fire the gas generating chemical reagent 32 arranged adjacent the detonator 33. The gas generating chemical reagent 32 so fired burns explosively, resulting in production of a large amount of high-temperature and high-pressure gas. This high-temperature gas instantaneously spreads from the gas compartment 12 inside the housing 11 of the pretensioner 10 to the chamber 14 inside the cylinder 13 so that the gas compartment 12 and the chamber 14 are filled up with the gas. As a consequence, the piston 15 is caused to abruptly move upwards within the cylinder 13 by a thrust of the expanding pressure of the gas, so that the wire cable 16 is pulled. As a result, the unillustrated take-up spindle around which the wire cable 16 is wound is caused to rotate in a webbing winding direction, whereby any slack in a webbing is taken up. Incidentally, the hammer pin 27 in the conventional gas generating device 90 has, as is shown in FIG. 3, a uniform diameter except that a free end portion thereof which strikes the detonator 33 is pointed and a longitudinal central portion thereof carries an upright flange against which the unillustrated inertia member collides. Further, the inner diameter D1 (see FIG. 4) of a hammer pin insertion hole 38 formed in the cover 37 is set substantially larger than the outer diameter of the hammer pin 27 so that any misalignment between an axis of the hammer pin trigger device 20 and that of the gas generator 30 can be tolerated to avoid contact between the hammer pin 27 and a wall of the hammer pin insertion hole 38 and hence any loss in detonator-striking energy. In the course of the assembly of the conventional gas generating device 90, specifically at the time point that the gas generator 30 has been held in place by the cover 37 subsequent to its placement inside the housing 1 as shown in FIG. 4, the detonator 33 is exposed to the outside through the hammer pin insertion hole 38 formed in the cover 37 and having the large inner diameter. If a worker should accidentally insert a self-tapping screw 39 or the like, which is employed for the assembly of the gas generating device 90 or for the mounting of the gas generating device 90 on the unillustrated webbing retractor, into the hammer pin insertion hole 38 and should then strike the detonator 33, the gas generator 30 is triggered to blow out high-temperature and high-pressure gas. This is certainly very dangerous to the worker. The conventional gas generating device 90 is therefore accompanied by the above-described potential problem. With the foregoing in view, the present invention has as a primary object the provision of a gas generating device which is free from any accidental triggering by a worker in the course of assembling or mounting work of the gas generating device. This object is achieved by the features in claim 1. According to the gas generating device of this invention, the inner diameter of the hammer pin insertion hole of the cover is formed smaller than the outer diameter of a bolt to be employed for assembling or mounting said gas generating device or that of a tool to be employed for assembling said gas generating device. This has made it possible to prevent accidental insertion of the bolt or tool into the hammer pin insertion hole during assembly work of the gas generating device or its mounting work on a vehicle body, thereby eliminating the potential danger that the gas generator could be triggered by an accidental strike of the detonator by the bolt or tool in the course of such work. The present invention is therefore effective not only for improving the preciseness of the assembling and mounting work of the gas generating device but also for heightening the safety of such work. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a gas generating device according to one embodiment of the present invention as applied to a webbing pretensioner; FIG. 2 is an enlarged fragmentary cross-sectional view of the gas generating device of FIG. 1; FIG. 3 is a cross-sectional view of a conventional gas generating device as applied to a webbing pretensioner; and FIG. 4 is a cross-sectional view illustrating a problem inherent to the conventional gas generating device. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT The gas generating device according to the one embodiment of the present invention will hereinafter be described with reference to FIGS. 1 and 2, in which elements of structure like the corresponding elements in the above-described conventional gas generating device are identified by like reference numerals and their description is omitted or simplified herein. As is illustrated in FIG. 1, the gas generating device according to this embodiment, which is generally indicated by a numeral 100, is different from the conventional gas generating device in that a cover 34 for holding the gas generator 30 within the housing 11 as well as a hammer pin 24, a spacer 23 and a hammer-pin-side cover 22 of the hammer pin trigger device 20 are formed in different shapes from the corresponding elements in the conventional gas generating device. The cover 34 in this embodiment, notably the inner diameter D2 of a hammer pin insertion hole 35 is dimensioned as depicted in FIGS. 1 and 2 to avoid accidental insertion of fastening members, such as bolts, self-tapping screws, pins and the like, and tools such as screw drivers, which are employed for assembling the gas generating device 100 of this embodiment or for mounting it on a webbing retractor. Described specifically, the inner diameter of the hammer pin insertion hole 35 can be set at a value smaller than 3 mm, for example, at about 2.5 mm or so because the nominal diameter of self-tapping screws having a smallest diameter among those employed for the assembly is 3 mm. As will be described subsequently herein, it is preferred to set the inner diameter of the hammer pin insertion hole 35 at a still smaller value, for example, at 1 mm or smaller if it is desired to minimize leakage of combustion gas of the gas generating reagent 32 toward a side of the hammer pin trigger device 20. In the illustrated embodiment, the cover 34 is provided with a cylindrical portion 36 so that the latter extends from the former toward a side of the hammer pin trigger device 20. This cylindrical portion 36 is arranged to align an axis of the gas generator 30 with that of the hammer pin trigger device 20, in other words, has centering function. Described specifically, the cylindrical portion 36 is constructed so that it extends toward the side of the hammer pin trigger device 20 and is internally fitted in a through-hole of the hammer-pin-side cover 22 of the hammer pin trigger device 20. Incidentally, the hammer pin 24 is arranged on the axis of the hammer pin trigger device 20, while the hammer pin insertion hole 35 is formed on the axis of the gas generator 30. As a consequence, the axis of the hammer pin 24 and that of the narrow hammer pin insertion hole 35 are precisely aligned so that the hammer pin 24 does not unnecessarily contact a wall of the hammer pin insertion hole 35. At a portion of the hammer pin 24, said portion extending toward the gas generator 30 from a flange portion 24a against which an inertia member 40 collides, the outer diameter of the hammer pin 24 is made smaller corresponding to the above-described hammer pin insertion hole 35, whereby a small-diameter portion 24b is formed. A further portion of the hammer pin 24, said further portion being located on an opposite side to the small-diameter portion 24b with respect to the flange portion 24a, is formed as a large-diameter portion 24c having a larger outer diameter than the small-diameter portion 24b so that the inertia member 40 is guided on and along the large-diameter portion 24c. Further, a through-hole formed in the spacer 23, in which through-hole the hammer pin 24 is slidably and supportedly fitted, has an inner diameter reduced corresponding to the outer diameter of the small-diameter portion 24b of the hammer pin 24 and has been machined accurately, so that a deviation of the axis of the hammer pin 24 from the axis of the hammer pin trigger device 20 is minimized. Owing to the above construction, the hammer pin 24 is free of the problem that the hammer pin 24 and the hammer pin insertion hole 35 may be misaligned and the hammer pin 24 may hence contact the wall of the hammer pin insertion hole 35. According to the gas generating device 100 of this embodiment, the inner diameter of the hammer pin insertion hole 35 formed through the cover 34 which holds the gas generator 30 within the housing 11 of the pretensioner 10 is made smaller than the outer diameters of bolts, screw drivers and the like employed in assembling and/or mounting work. This has made it possible to avoid the potential danger that a worker may insert one of such bolts, screw drivers and the like into the hammer pin insertion hole 35 to accidentally strike and trigger the gas generator 30. It is therefore possible to avoid accidental triggering of the gas generator in the course of assembling or mounting work. The potential danger of the above-mentioned accidental triggering during work has therefore been eliminated successfully. In the present embodiment, the cylindrical centering portion 36 which is arranged on the cover extends toward the hammer pin trigger device 20 and is fitted in the hammer-pin-side cover 22. It is therefore possible with extreme ease to have the axis of the hammer pin insertion hole 35 aligned precisely with that of the hammer pin 24 and vice versa. This prevents the hammer pin 24 from accidentally contacting the wall of the hammer pin insertion hole 35 so that the hammer pin 24 is assured to strike the detonator 33 in the event of an emergency. Moreover, the smaller inner diameter of the hammer pin insertion hole 35 has brought about such a secondary advantage that high-temperature and high-pressure gas formed as a result of explosive burning of the gas generating chemical reagent 32 does not leak out toward the hammer pin trigger device 20 through the hammer pin insertion hole 35.

Claims: A gas generating device comprising: a hammer pin; a gas generator (30) having a detonator (33) accommodated in a housing (11) for being fired when struck by said hammer pin (24); and a hammer pin trigger device (20) for causing said hammer pin to strike said detonator in the event of an emergency of a vehicle on which said gas generating device is mounted; wherein said gas generator has a cover (34) arranged to substantially close up said gas generator on a side of said hammer pin trigger device and defining therethrough a hammer pin insertion hole (35) into which said hammer pin (24) is inserted, and said hammer pin insertion hole of said cover has such a small inner diameter that no fastening member to be employed for assembling or mounting said gas generating device can be inserted in said hammer pin insertion hole (35), wherein said hammer pin (24) has a small-diameter portion (24b) located on a side of said detonator and capable of being inserted into said hammer pin insertion hole of said cover, and a large-diameter portion (24c) extending from said small-diameter portion toward a side opposite to said detonator, characterised in that said hammer pin trigger device (20) has a bottom-closed, substantially cylindrical housing member (21), a hammer-pin-side cover (22) is arranged on a side of an opening of said housing member and a spacer (23) is arranged on an inner side of said hammer-pin-side cover (22), that said spacer (23) centrally defines a through-hole to permit extension of said hammer pin (24) therethrough, and said through-hole has an inner diameter substantially equal to an outer diameter of said small-diameter portion (24b) of said hammer pin (24). A gas generating device according to claim 1, wherein said hammer pin trigger device (20) has an inertia member (40) arranged displaceably thereon, the inertia member being displaced upon application of a deceleration of at least a predetermined value thereon, said hammer pin (24) has a small-diameter portion (24b) located adjacent said detonator, a contact portion (24a) with which said inertia member is brought into contact and a large-diameter portion (24c) extending from said contact portion to an opposite side, and said inertia member (40) is guided on and along said large-diameter portion (24c). A gas generating device according to claim 1, wherein said inner diameter of said hammer pin insertion hole (35) is smaller than 3 mm. A gas generating device according to claim 1, wherein said hammer pin (24) is arranged on an axis of said hammer pin trigger device (20), said hammer pin insertion hole (35) is formed on an axis of said gas generator (30), said gas generator (30) and said hammer pin trigger device (20) are provided with first and second centering means (36,22), respectively, and said first and second centering means (36,22) are mutually engageable to align said axis of said gas generator (30) with that of said hammer pin trigger device (20). A gas generating device according to claim 4, wherein said first and second centering means (36,22) are a cylindrical portion (36) extending from said cover (34) of said gas generator (30) toward the side of said hammer pin trigger device (20) and a hammer-pin-side cover (22) arranged on said hammer pin trigger device (20) and engageable with said cylindrical portion (36), respectively. A gas generating device according to claim 5, wherein said hammer pin trigger device (20) has a bottom-closed, substantially cylindrical housing member (21) and a hammer-pin-side cover (22) arranged on a side of an opening of said housing member, and said cylindrical portion (36) extending from said cover (34) of said gas generator (30) is engageable with said hammer-pin-side cover (22).

Inventors: IKESUE HARUYUKI, MATSUKI MASUO, IKESUE, HARUYUKI, MATSUKI, MASUO
Applicants: NSK LTD, NSK LTD.
Application year: 1994
Main classification: B60R22
IPC codes: B60R22, B60R21, B01J7